Cyprian of Carthage, Epistle 69.3
To accept the baptism of heretics and schismatics is to endorse what they have done. There can be no empty part alongside a valid part. If someone can baptize, they can also give the Holy Spirit. But if they cannot give the Spirit, because they stand outside the Spirit, they cannot baptize anyone, since there is one Baptism, one Holy Spirit, and one Church founded by Christ the Lord on Peter as the source and reason for unity. It follows that, because everything they do is empty and false, we ought not to approve any of their actions. What could be ratified and firm before God if it is done by those whom the Lord calls his enemies and adversaries in his Gospel, saying, "Whoever is not with me is against me, and whoever does not gather with me scatters" (Matthew 12:30)? The blessed apostle John, keeping the Lord's commands and precepts, writes in his letter, "You have heard that the antichrist is coming. Even now many antichrists have appeared; from this we know that it is the last hour. They went out from us, but they were not of us; for if they had been of us, they would have remained with us" (1 John 2:18-19). We must therefore ask whether those who are adversaries of the Lord and are called antichrists can confer the grace of Christ. Since we are with the Lord, hold his unity, and administer his priesthood in the Church according to his will, we must repudiate and reject as profane whatever his adversaries and antichrists do. To those who come from error and wickedness yet recognize the true faith of the one Church, we must give the sacraments of divine grace and the truth of unity and faith. We wish you, dearest brothers, always to be well.
Latin
Caeterum probare est haereticorum et schismaticorum baptisma consentire in id quod illi baptizaverint. Neque enim potest pars illic inanis esse et pars praevalere. Si Baptizare potuit, potuit et Spiritum sanctum dare. Si autem Spiritum sanctum dare non potest, quia foris constitutus cum sancto Spiritu non est, nec baptizare venientem potest, quando et Baptisma unum sit, et Spiritus sanctus unus, et una Ecclesia a Christo Domino super Petrum origine unitatis et ratione fundata. Ita fit ut cum omnia apud illos inania et falsa sint, nihil eorum quae illi gesserint probari a nobis debeat. Quid enim potest ratum et firmum esse apud Deum quod illi faciunt quos Dominus hostes et adversarios suos dicit in Evangelio suo ponens: Qui non est mecum adversum me est; et qui non mecum colligit, spargit. Et beatus quoque apostolus Joannes mandata Domini et praecepta custodiens in epistola sua posuerit, dicens: Audistis quia antichristus venit. Nunc autem antichristi multi facti sunt. Unde cognoscimus quia novissima hora est. Ex nobis exierunt, sed non fuerunt ex nobis. Si enim fuissent ex nobis, mansissent utique nobiscum. Unde nos quoque colligere et considerare debemus an qui adversarii sunt Domini, et appellati sunt antichristi, possint dare gratiam Christi. Quare qui cum Domino sumus, et unitatem Domini tenemus et secundum ejus dignationem sacerdotium ejus in Ecclesia administramus, quaecumque adversarii ejus et antichisti faciunt repudiare et rejicere et pro profanis habere debemus, et eis qui de errore et pravitate venientes agnoscunt unius Ecclesiae veram fidem, dare illis per omnia divinae gratiae sacramenta et unitatis et fidei veritatem. Optamus vos, fratres charissimi, semper bene valere.